1. Field of the Invention
The invention relates to a body detection apparatus and a body detection method. Mores specifically, the invention relates to a body detection apparatus that is mounted in a vehicle and is capable of appropriately grouping bodies that are approaching to the vehicle from neighboring areas, and such a body detection method.
2. Description of the Related Art
In recent years, a vehicle, such as a passenger automobile or the like, is equipped with a vehicle-mounted radar device that detects other vehicles, pedestrians, road-installed bodies, etc., that are present around the vehicle (hereinafter, referred to as “host vehicle”). The vehicle-mounted radar device detects a target that is approaching to the host vehicle from the front or a side of the host vehicle, and measures a relative distance, and a relative speed of the target relative to the host vehicle, as well as the direction (direction angle) in which the target, that is, the object body, exists, etc. Then, on the basis of results of detection, the vehicle-mounted radar device determines a risk of collision between the host vehicle and the target. An example of the foregoing vehicle-mounted radar device is a radar device disclosed in Japanese Patent Application Publication No. 8-160132 (JP-A-8-160132).
The vehicle-mounted radar device sometimes obtains a plurality of acquisition points when bodies present around the host vehicle are detected. An example of the case where the vehicle-mounted radar device obtains a plurality of acquisition points is a case where a plurality of vehicles are present around the host vehicle, and acquisition points are obtained from each of the plurality of vehicles.
Besides, in some cases, the vehicle-mounted radar device detects one vehicle present around the host vehicle, and detects a plurality of acquisition points from the one vehicle (since the vehicle is a body having a certain size). For example, in the case where a target is a large-size vehicle, such as a bus, a truck or the like, acquisition of a plurality of acquisition points from a single vehicle is remarkably often seen, in comparison with the case where the target is a passenger automobile.
Therefore, a common vehicle-mounted radar device performs a grouping process of estimating acquisition points detected by the vehicle-mounted radar device as being a single body on the basis of characteristics of the acquisition points.
For example, the radar device disclosed in JP-A-8-160132 finds a radius of curvature (curved line) along which the host vehicle is traveling, and finds a distance D from each acquisition point acquired by the radar device installed in the host vehicle to the curved line, and an angle θ of a line extending from the acquisition point to a center of a front portion of the host vehicle with respect to a forward axis direction of the host vehicle. Then, acquisition points that are similar to one another in the distances D and the angle θ are grouped together, and are estimated to be of a single body.
Concretely, as shown in FIG. 14, in the case where a plurality of acquisition points (an acquisition point P1 and an acquisition point P2 shown in FIG. 14) are obtained, the radar device disclosed in JP-A-8-160132 compare differences between distances D (distance D2−distance D1) from the acquisition points to a curving line R and differences between angles θ (angle θ2−angle θ1) with respect to the plurality of acquisition points. Then, the radar device disclosed in JP-A-8-160132 groups an acquisition point P1 and an acquisition point P2 together if distance D2−distance D1≦threshold value D, and the angle θ2−angle θ1≦threshold value θ. That is, the radar device estimates that the acquisition point P1 and the acquisition point P2 have been obtained from a vehicle 1 (a single body).
However, according to the radar device disclosed in JP-A-8-160132, there is possibility of estimation of acquisition points of a plurality of bodies as being in one group (being of a single body), depending on the positions of the bodies, or the traveling directions thereof. For example, let it assumed that, as shown in FIG. 15, a vehicle 2 and a vehicle 3 are present forward of the host vehicle, and the vehicle 2 and the vehicle 3 are detected by a radar device. As shown in FIG. 15, if distance D4−distance D3≦threshold value D, and angel θ4−angle θ3≦threshold value θ, there is possibility of the radar device grouping the acquisition point P3 and the acquisition point P4 together, and estimating the acquisition point P3 and the acquisition point P4 as having being obtained from a single body. That is, the radar device disclosed in JP-A-8-160132 may possibly estimate a plurality of vehicles as being one and the same vehicle in a case where the vehicles are moving adjacent to each other, or the like. Therefore, this related-art radar device is not able to always perform the grouping with sufficient accuracy.